Radio echo training system



SePf- 22, 1953 R. L.. GARMAN Er AL RADIO 66H0 TRAINING SYSTEM 2Sheets-Sheet l Filed May 24, 1946A III-III.' I

INVENTORS NRAYMOND L. GARMAN BQ/URTIS R. HAUPT i 2 Sheets-Sheet 2 FiledMay 24, 1946 m s R M T www mi y VLH. M WDR w WS wm AU Rc www Yom w Nm.San u o E. .zmw wml@ mmsqum :9E r

, mm :Sim om Patented Sept. 22, 1953 AUNITED STATES PATENT OFFICERADIoEoHo TRAINING SYSTEM Raymond L. Carman, Pleasantville, N. Y., andCurtis R. Haupt, San Diego, Calif., assignors, by mesne assignments, tothe United States of America as represented by the Secretary of WarApplication lMay 24, 1946, Serial No. 672,024

16 Claims.

This invention relates generally to electrical .apparatus andparticularly to training equipment for airborne P. P. I. systems.

It is often desirable to reproduce, ,for training and other purposes,areas searched and targets located by a radio echo detection (radar)system. Such a simulated reproduction can ,greatly reduce the effort andtime involved in training operators.

While such simulation is relatively simple for systems using certaintypes of indicators, simula- -tions for systems using plan positionindication (P. P. I.) present more of a problem due to the complexity ofreturned echo signals, For example, returned echoes as seen in P.. P. I.may repre- .sent water and various types of land masses which have.different characteristic signals. If the radar system is airborne thereis also the problem Aof properly simulating electromagnetic beamcoverage in the vertical plane.

It is thereforeV an object of this invention to generate Ysignalssimulating lland masses and ground clutter.

Another object is to generate video target signals in proper azimuthwith an intensity proportional to range.

Another object is to simulate such signals to ,portray the effect ofelectromagnetic `beam coverage in a vertical plane.

f A further object is to generate signals for simulating the effect ofbeam widthand intensity.

A still further object is to provide means for combining and presentingthe above simulated signals in P. P. I. fashion.

,Other objects, features, and advantage of the `invention will suggestthemselves to those skilled in the art and will be apparent from thefollowing description of the invention taken in connection with theaccompanying drawings in which:

jFig. l is a block diagram illustrating a circuit embodying theinvention;

Fig. 2 is a view of the P. P. I. screen indicating faded areas due tobeam coverage in the vertical plane;

Fjig. 3 is a view of the P. P. I. screen `indicating beam width andintensity with respect to range; and

Fig. 4 shows a schematic circuit diagram more specifically illustratingcertain components of Fig. l.

The apparatus here described includes a transmitting cathode ray tubewhich, together with associated apparatus and a map made upon positivenlm, functions to produce upon a receiving cathode ray tube indicator asimulation of land and water areas as -they would normally be observed`-upon an actual airborne radar indicator. Further circuits in theapparatus achievesimulation of the variation of echo signal dimensionsand intensity as seen upon an actual radar indicator, ,.and of certaininterference knownin Ythe 2 art as ground clutter which tends to obscureAetals on the screen.

Referring now to Fig. l, the indicator control central (synchronizer) l)and scanner Il provide electrical and mechanical synchronizing means,respectively, for the trainer system. Synchronizer vl0 may be a masteroscillator such as that shown on page 142 of Radar System Fundamentals,,NAVSI- IIPS` 900,017, published by the Navy Department in k1944. Asharpened trigger pulse l2 from synchronizer I0 actuates a sweepgenerator 3 which, in conjunction with a rotating yoke it, driven Abyscanner Il, provides a transmitting cathode ray tube (C. R. T.) l5 withplan position V.indication (P. P. I.) scan. The visible trace presentupon the screen of .transmitting rC. E. T. i5 is focused -by a lens I6on a positive ii-lm Sl' of ,a desired map, permitting light to pass morereadily through those areas from which simulatedsignal reflections aredesired than from other areas. ',Ilie light passing through film i? isin turn focused :by a lens I8 on astabilized photomultiplier tube I9which vgenerates video signals according tothe variation in intensity ofthe light received. This simulated land mass signal is amplified inanlampliiier 20, and combined with noise signals .from a variable gainnoise ampliigier 2| in anamplier 22. A suitable noise generator andamplifier is shown in the patent to lRing et al., No. 2,165,509, issuedon July ll, 1939. Another suitable noise generator is shown inMassachusetts Institute of Technology Radiation `Iceberatory Report No.4513, dated `September 17, l1943. Target echo signals from a targetsimulating circuit later lto be described, are also combined with theland mass land noise signals in amplifier 22, and then theentirecombined signal is passed through a, limiter rstage 23 to intensitymodulate `the control grid* 24 of a receiving C. R..'T. 25. Asuitablelimiter stage. 23 is shown on page 159 of Radar ElectronicsFundamentals, NAVSHIPS 900,016, published by the Navy Department fin194.4. 'Ifhe noise signal from variable gain amplifier 2| is for thepurpose of simulating yground clutter of the area scanned, and maybeadjusted to simulate varying transmitting and receiving c QnditiQns.

lThe target echo simulating circuitcomprises a positive grid short.delay multivibrator 25 actuated by pulse l2 from synchroniser l0.Multivibratorlt produces a positive gate output pulse 21 having itstrailingedge.accurately controllable in time phase by a pulsewidthchanger 28. This pulse width variation represents variation in rangewhich may be manually introduced, The trailingedge of the gating pulse2l trips a microsecond pulse generator 29 vproducing a video target echopulse30 which is passed through a clipperstage 3l anda potentiometer 32to be combined with land mass Yand ground clutter signals in amplifier22. Clipper stage 3| is shown in Fig. 4, and consists of a diode 1Ihaving a source of bias 13 in its cathode circuit. Bias source 13 isconnected at terminal 12 to the cathode of diode 1| and is alsoconnected through terminal 14 to ground, thus placing a positive biasupon the cathode of diode 1 I. The output from pulse generator 29 is fedinto terminal v15 and then through a resistor to the anode of diode-1I..Theclipped pulses from pulse generator 29 are taken out at terminal 1of clipper 3| and are fed into potentiometer 32. To cause this pulse to4trace only a short arc on C. R. T. 25, the clipper stage 3| is normallybiased at cut-off and a rotaryswitch 33,' having adjustable contacts anddriven by scanner I I, intermittently shorts out the bias to causetarget indication at an azimuth'deter'mined bysettings of the adjustablecontacts.y i A suitable rotary switch having adjustable contacts isshown in the patent to Barr, No. 1,793,989, issued lon February 24,1931. This switch is illustrated in Fig. 4 and comprises a rotary switch33 having two conductive drum halves 6I andl 62, separated by aninsulator bar 55. Adjustable contacts 63 and 64 are adapted to slideWithin groove 6B on the surface of said drum. A shaft t!!` ismechanically coupled to the shaft being driven by scanner Il, and theshaft Gil-causes drum il, 62 to be driven in synchronism with thevscanning of cathode ray tubes I and 25. f Adjustable contact 63 isgrounded at a terminal 66. and adjustable contact 64 is connected toterminal E1 which is in turn connected to terminal 12 in the cathodecircuit of diode 1I in the clipper stage 3|. As rotary switch 33 isdriven by scanner Il, it will be apparent that at a given angle ofrotation of drum 6I, 62 both adjustable contacts 63 and 64 will be uponthe same side of insulator 65, and for that interval of time bias source13 within clipper stage 3| will be short-circuited by the rotary switch33, the short circuit being through terminal 12, through terminal 61,through contact 64, through drum-half 62, through -contact 63, andthrough terminal 66 to ground. Since bias source 13 is grounded atterminal 14 it willbe seen that it is shorted out periodically by rotaryswitch 33. By movingv contact 64 closer or further from'contact E3, theangle of rotation of drum El B2 necessary `before bias source 13'islshort-circuited may be increased or decreased. During the interval whenbias source 13 is short-circuited, pulses from pulse generator '29 arepassed by diode 1I, and placed upon potentiometer 32. -The potentiometer32 is mechanically linked to the pulse width changer 28 in a manner toenable automatic decrease of signal strength with range.

A precision long delay multi-vibrator 35 is also triggered by thetrailing edge of gate pulse 21 to produce another gate pulse 36 alsocontrollable in time phase by pulse width changer 28, which is passedthrough a distorter stage 31`. The distorter stage may consist of acathode'follower properly biased to produce a distorted signal 38. Fromthe shape of this signal it is seen Vthat when applied p to theintensity control grid 24 of receiving C. R. T. 25, it will produce anuneven illumination on the screen such as illustrated in Fig. 2. Thisuneven illumination simulates electromagnetic beam coverage in thevertical plane. The vvariation in pulse width is representative of thevariations in the angle that the beam makes with the vertical..

Receiving C`. R. T. 25 is provided with P. P. I. scan by conventionalsweep generating means indicated in the block 39 including, as shown, asweep gate multivibrator, sweep generator,r and a sweep amplifier,actuated by synchronizer I0 and coupled to the horizontal vand verticaldeflection plates through a rotary transformer 40, mechanicallyconnected to scanner II, and conventional clamper and driver stages 4|and 42. Suitable transformer and clamper stages are shown connectedtogether and are described on pages 282, 283 of the aforesaid RadarSystem Fundamentals. The electrical and mechanical connections tosynchronizer Wand scanner I I, respectively, provide a P. P. I. scansynchronized with that of transmitting Ci. R; T. I5.

In many radar systems, objects which are of the same size cause anindication to appear on the indicator screen smaller in azimuth anglewith increasing distance. In attemptingV to simulate this effect it isdesired to produce' a beam-on the face of cathode ray tube 25whichwilldwell for .ia

longer period of time at its 'azimuthal center than lmuth'al and tubeface -extremities less energyffis returned from the target. ReferringnowtoFig. 3, this effect is simulated by modifying the ytypeof sweep fromradial straight-line sweep' to'one having theappearance of linearlymodulated .oscillations centered about an imaginary straight line butincreasing substantially linearly in amplitude -with increasing range.As shown in Fig.V 1,'-in

order to obtain the desired effect, anoscillator 49, operating forexample at kilocycles, produces a vsine wave outputY 50. This signal,passed through a distortion-amplifier. 5|,"arrives1 as a square wave 52at'a modulator 53;,where itv is lmodulated by a sawtooth wave 54 from asawtooth generator 55'. The sawtooth generator `55 is triggered bysynchronizer Ill. vThe output of modulator 53 is a linearlyincreasing'square wave 56 which is further modified in a differentiator51 to produce differentiated square wave pulses 58. The purpose ofpulses 58 is to cause the electron beam of the C. R. T. to sweep at aSlowerrate near the imaginary straight line sweep, when near the centerofthe P. P. I. tube, thereby simulating the `effect of lesser `intensityreturns'at the sides of the transmitted energy beam. However, near the'tube periphery, the beaml moves so rapidly at a distance a similary arcfrom the center line, that only when the echo occurs near the centerline does the screen become illuminated. The output ofdiferentiator 51is modulated into sine and cosine envelopes by the sine and cosinepotentiometers 59 andl respectively, which are 'drivenby scanner II, andthence applied to the horizontal and vertical deection circuits ofreceiving C.R.T.25. i

It will be seen that the trainer circuit herein set forth 'provides forsimulating realistic operation of a radar system,

While there has been described what is at presentconsidered to -be thepreferred embodiment of this invention', it will be obvious to thoseskilled inthe art that various changes and modications may be madetherein without departing from the scope and spirit of the inventio asset forth in the appended claims.

What is claimed is:

l. A radio echo training system comprising cathode ray tube indicatormeans, means vfor simulating ground echo signals and comprising a filmmap of the terrain that it is desired to depict upon the face of saidindicator means and means for scanning said map so as to produce signalslto be impressed-upon-the lf'ace'of said indicator means, means forsimulating target echo signals, and means for combining both saidsignals upon the face of said indicator means.

2. The system of claim 1, including means for synchronizing theoperation of said scanning means with that of said indicator and targetecho simulating means.

3. The system of claim 2, wherein said scanning means includes cathoderay tube indicator means having its face facing one side of said film,and photoelectric cell means facing the other side of said nlm, saidsynchronizing means comprising a pulse generator for activating saidtarget echo simulating means as well as the sweep circuits of both saidindicator means.

4. A radio echo training system comprising: means for scanning a terrainmap so as to produce simulated ground echo signals, said scanning meansincluding first plan position indicator means; second plan positionindicator means; means for generating simulated, variably delayed targetecho signals; means for synchronizing the sweep circuits of said firstand second indicator means togetherV with the means for generatingtarget echo signals; and means for combining said simulated target andground echo signals upon the face of said second indicator means.

5. I'he system of claim 4, further including means for generating noisesignals, and means for impressing said noise signals upon the face ofsaid second indicator means.

6. The system of claim 5, further including means coupled to said meansfor generating target echo signals and to said means for generatingnoise signals for varying the signal-tonoise ratio in accordance withthe range of said target echo signals so as to decrease target echosignal strength with increases in range.

7. A radio echo training system comprising: means for scanning a terrainmap so as to produce simulated ground echo signals, said scanning meansincluding rst plan position indicator means; second plan positionindicator means; means for synchronizing the sweep circuits of saidfirst and second indicator means; means for generating simulated targetecho signals including multivibrator means adapted to be activated bysaid synchronizing means, means for varying the duration of the squarewave output of said multivibrator means, and pulse producing meansadapted to be triggered by the trailing edge of said square wave output;and means for combining said simulated target and ground echo signalsupon the face of said second indicator means.

8. The system of claim '7, further including l means for generatingnoise signals, and means for placing said noise signals upon the face ofsaid second indicator means.

9. The system of claim 8, further including means coupled between saidmeans for generating target echo signals and said means for generatingnoise signals for varying the signal-tonoise ratio in accordance withthe range of said target echo signals, so as to decrease target echosignal strength with increases in range.

10. The system of claim 7, further including means for unevenlyilluminating the face of said second indicator means, said illuminatingmeans comprising multivibrator means adapted to produce an output squarewave whose duration is also varied by said varying means, said lastnamedmultivibrator means being triggered by the output of said rst-namedmultivibrator means.

11. The system of claim 7, further including square wave oscillatormeans, means for coupling the output of said square wave oscillatormeans to the output of the sweep circuit of said second indicator meansto produce a combined output waveform, and means for dilerentiating saidcombined output waveform and then applying it to the face of said secondindicator means in order that said simulated target echoes may appearmore brightly near the azimuthal center and beginning than near theazimuthal extremities and end of the sweep.

12. The system of claim 7, wherein said synchronizing means alsoincludes scanner means adapted to rotate the sweeps appearing upon thefaces of said first and second indicator means, and wherein said systemfurther includes switch means adapted to be rotated by said scannermeans, said switch means being coupled to said pulse producing means andserving to allow the pulse output thereof to appear upon the face ofsaid second indicator means for only a small azimuth angle.

13. The system of claim 12, further including square wave oscillatormeans, means for coupling the output of said square wave oscillatormeans to the output of the sweep circuit of said second indicator meansto produce a combined output waveform, and means for differentiatingsaid combined output waveform and then applying it to the face of saidsecond indicator means in order that said simulated target echoes mayappear more brightly near the azimuthal center and beginning than nearthe azimut al extremities and end of the sweep. l

14. The system of claim 13, further including means for generating noisesignals, and means for placing said noise signals upon the face of saidsecond indicator means.

15. The system of claim 14, further including means adapted to be variedby said means for varying and coupled between the output of said firstmultivibrator means and said second indicator means for decreasing theamplitude ofthe output of said first multivibrator means with increasesin target range in order to vary the signalto-noise ratio.

16. The system of claim 15, further including means for unevenlyilluminating the face of said second indicator means, said illuminatingmeans comprising multivibrator means adapted to produce an output squarewave whose duration is also varied by said varying means, said lastnamedmultivibrator means being triggered by said first-named multivibratormeans, and means coupled to the output of said last-named multivibratormeans, for distorting the output thereof before its application to saidsecond indicator means.

RAYMOND L. GARMAN. CURTIS R. HAUPT.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,199,066 Bernstein Apr. 30, 1940 2,215,365 Vestergren Sept.17, 1940 2,399,661 Bowie May 7, 194:6 2,405,591 Mason Aug. 13, 19462,406,751 Emerson Sept. 3, 1946 2,415,831 Marshall Feb. 18, 19472,416,088 Deerhake Feb. 18, 1947 2,433,681 Blumlein Dec. 30, 19472,539,511 Hansen Jan. 30. 1951

